Cooled gas turbine blade

ABSTRACT

Described is a cooled gas turbine blade with a shroud ( 2 ) in which a cooling channel system (K) is provided, which is closed off radially to the gas turbine blade with a cover plate ( 6 ).  
     The invention is characterized in that the cover plate ( 6 ) has a circumferential edge, along the entire extension of which the cover plate ( 6 ) enters into a continuous shape-mated connection or a plurality of locally limited shape-mated connections with the shroud ( 2 ).

FIELD OF TECHNOLOGY

[0001] The invention relates to a cooled gas turbine blade with a shroudin which a cooling channel system is provided, which is closed offradially to the gas turbine blade with a cover plate.

STATE OF THE ART

[0002] In an effort to increase the efficiency of turbine powermachines, in particular of gas turbine systems, the achieving of thehighest possible combustion temperatures plays an especially importantrole, in particular since this allows a direct optimization of thethermal efficiency of the combustion process. High combustiontemperatures have the result, however, that the gas turbine componentsexposed to the hot gases generated during the combustion process arealso subject to extremely high thermal loads on the material. Thelatter, at the same time, constitute the current technical limits for apotential further increase of the combustion temperatures, especiallysince the temperatures that can be achieved inside the combustor are farabove the thermal load limits of those materials of which the gasturbine components in the hot channel of the gas turbine are made, mostof all the gas turbine blades.

[0003] In order to be able to nevertheless increase the thermal loadlimits of the system components in the hot gas channel, in spite ofexisting, material-specific maximum temperatures, the heat-exposedsystem components are actively cooled by means of a targeted supply ofcooling air by providing corresponding cooling channel systems. Asalready mentioned above, the gas turbine blades positioned downstreamfrom the combustor require, as a result of the high thermal load, highlyeffective cooling measures in order to not exceed the material-specifictemperature limits necessary for continuous operation inside the bladearrangements.

[0004] In an actually known manner, gas turbine blades, regardless ofwhether they are rotating or guide blades, usually consist of a bladeroot and a blade hub, where in most cases a shroud projects radiallyover the blade hub. The cooling system provided inside a gas turbineblade usually consists of a plurality of individual cooling channelsthat extend from the sides of the blade roots radially through theentire turbine blade up to the shroud. Within the shroud, coolingchannel areas are provided, in which flow guidance structures forremoving and deflecting cooling air are provided in order to improve thecooling effect inside the shroud.

[0005] For reasons resulting from the casting process during the bladeproduction, a turbine blade existing as a semi-finished productfollowing the casting process and the removal of the casting core thatproduces, among other things, the cooling channels, is provided inparticular in the area of the shroud with large openings that permit alater insertion of the previously mentioned flow guidance structures,for example an impact cooling plate, which must be sealed, however, soas to be gas-tight. For this purpose, a closing plate or so-called coverplate, which is largely adapted to the opening contour, is used, saidclosing plate usually being connected with the shroud of the gas turbineblade by way of high-temperature soldering.

[0006]FIG. 2a to 2 c illustrate an actually known connection between acover plate 6 and the shroud 2 of a turbine blade. FIG. 2a shows aperspectival illustration of a turbine blade with a blade hub 1 and ashroud 2. The shroud 2 has two side edges 4 and 5, each of which isconstructed with a groove contour 3, along which a cover plate 6 isinserted in a shape-mated manner. The cross-section according to sectionline S1 is shown in FIG. 2b. The groove contour 3 partially covers thecover plate 5 inserted into the shroud 2, said cover plate being fixed,in addition to the shaped-mating between the groove contour 3 and thecover plate 6 by way of a soldering connection 7. The cross-sectionillustration according to FIG. 2b shows the cooling channels K enclosedbetween the cover plate 6 and the shroud 2, through which coolingchannels the cooling air is fed through the cooling system (not shown infurther detail) inside the gas turbine blade.

[0007] If a break inside the soldering joint (7) occurs along the jointconnection that is shape-mated and incorporated into the material alongthe side edges 4 and 5, the cover plate 6 along side edge 4 is unable todetach because of the existing shape-mating of the shroud 2. Thesituation is different, though, along the front and backside edges 8 and9 in FIG. 2a, the associated section of which side edges along sectionline S2 is illustrated in FIG. 2c. Along the side edges 8 and 9, thecover plate 6 is joined with the shroud 2 only by a soldering connection7 by way of a metallurgical joint. There is no additional shape-matingin this case. If, however, tears occur inside the soldering joint 7 inthe area of this joint connection as a result of the high thermal loads,as well as mechanical deformation created during the operation of a gasturbine, this inevitably results in local detachments between the coverplate 6 and the shroud 2, which finally lead to the total loss of thecover plate 6. Such a cover plate loss leads to catastrophic damage inthe gas turbine system, however, which requires the system to be stoppedin order to be able to perform extensive repair work.

DESCRIPTION OF THE INVENTION

[0008] The invention is based on the objective of constructing a cooledgas turbine blade with a shroud in which a cooling channel system isprovided that is closed off radially to the gas turbine blade in such away that the cover plate is joined with the shroud in a secure manner,and in which the previously mentioned total loss of the cover plate canbe excluded. Another objective is to decisively minimize losses due toleakage in the case of tears occurring in the joint connection betweenthe cover plate and the shroud. The measures to be instituted herebyshould require only a small expenditure for construction, which wouldnot or would only insignificantly increase the manufacturing costs ofcooled gas turbine blades.

[0009] The solution for this objective is disclosed in Claim 1. Thecharacteristics that advantageously further develop the concept of theinvention are the subject of the secondary claims and specification inreference to the exemplary embodiments.

[0010] According to the invention, a cooled gas turbine blade accordingto the preamble of Claim 1 is constructed in such a way that the coverplate has a circumferential edge, along the entire extension of whichthe cover plate enters into a continuous shape-mated connection or anumber of locally limited shape-mated connections with the shroud of thegas turbine blade.

[0011] Starting with the initially described state of the art accordingto the gas turbine blade illustrated in FIG. 2a ensures only ashape-mated connection between the cover plate and the shroud at twofacing side edges because of the receptacle groove existing there, theobjective is to also provide corresponding shape-mated connections alongthe other two side edges, so that the cover plate enters, if possible, ashape-mated connection with the shroud of a gas turbine blade along itsentire circumferential edge.

[0012] Due to construction and assembly, this requirement cannot befulfilled with the actually known gas turbine blade according to FIG.2a, especially since the cover plate is pushed into the receptaclegroove 3 sideways, longitudinally to the side edges 4 and 5 forassembly. Any later attachment of corresponding, groove-shapedlongitudinal ridges along the side edges 8 and 9 on the shroud 2illustrated in FIG. 2a would decisively increase the total expenditurein the production of the gas turbine; additionally, the soldering jointsneeded for the attachment of such potential lateral ridges representadditional mechanical “breakaway points.”

[0013] In contrast, a shroud constructed according to the inventionprovides a receptacle contour adapted to the shape and size of thecircumferential edge in the sense of a box edge, into which the coverplate can be completely inserted radially. The receptacle contourpreferably has a stepped cross-section, comparable to that of a pictureframe, into which a picture can be placed from the back. The steppedcross-section of the receptacle contour hereby has radially or obliqueradially-oriented a first stage surface, and axially-oriented a secondstage surface, the so-called support surface, on which the cover platecan be placed with its entire circumferential edge. The directionalinformation of radially or axially hereby refers to the usualdirectional information commonly used in connection with an axial flowrotor arrangement inside a gas turbine system. Between thecircumferential edge of the cover plate inserted into the receptaclecontour and the radially or oblique radially-oriented first stagesurface, a gap is provided into which a joining means, preferablysoldering material, can be inserted. The soldering material ispreferably selected so that it has no or only little ductility followingthe performance of the soldering and/or thermal treatment process, i.e.is brittle.

[0014] Because of thermally produced deformations, the brittlenessinherent in the soldering material causes tears inside the solderingseam even at the beginning of the first operation of the gas turbineblades, which form as “zig-zag”-shaped break lines or areas and extendthrough the entire soldering joint. Surprisingly, it is especially thesebreak surfaces that form which ensure a safe shape-mating and also helpin creating a soldering joint free of bending stresses between the coverplate and the shroud.

[0015] The hair-line tear forming in the soldering joint basicallypresents a cooling air leak, through which cooling air is able to escapefrom the cooling air system in the gas turbine blade defined by thecover plate towards the outside; however, this cooling air loss isnegligibly small and is not significant. In addition, oxidation layersform on the surfaces of the tear in the soldering joint, which oxidationlayers are able to reduce, on the one hand, the gap produced by thetear, and, on the other hand, ensure a play-free seat of the cover platein the shape-mated connection established by the soldering joint, inspite of the large vibrations occurring during the operation of the gasturbine.

[0016] Further details regarding the above described shape-matedconnection, which is based on the formation of a tear in the solderingjoint that completely surrounds the cover plate, are found in thefurther description in reference to the following exemplary embodiments.

[0017] According to the invention, alternatively to a soldering jointand a hairline tear forming in it in order to produce a seat of thecover plate free of play and bending stresses inside the shroud, amechanical retention means that enters both into a functional connectionwith the shroud as well as with the cover plate is suitable.

[0018] In a simple embodiment, the first, preferably radially-orientedstep surface of the receptacle contour inside the shroud for thispurpose provides a circumferential mounting groove, with which theoutside contour of a retainer ring that surrounds the cover plate in asuitable form is able to engage at least half-way. An insertion of thecover plate into the receptacle contour of the shroud is brought aboutby a mechanical tying together of the retainer ring, which, afterappropriate joining inside the mounting groove is able to spread in theshroud and in this way ensures a shape-mated connection between theshroud and the cover plate. Alternatively to the use of a retainer ring,rod-shaped retention means can also be used to create a shape-matedconnection between the cover plate and the shroud by inserting themthrough suitable holes in the cover plate and the shroud. The rod-shapedretention means may be inserted in corresponding mounting openings so asto extend tangentially or radially between the cover plate and theshroud. Although the cover plate in this way is not joined along itsentire circumferential edge by means of a continuous shape-matedconnection with the shroud, as is the case with a circumferentialsoldering joint, this method, however, also ensures a secure seat of thecover plate in the shroud.

BRIEF DESCRIPTION OF INVENTION

[0019] The invention is described below as an example, using exemplaryembodiments in reference to the drawings without limiting the generalidea of the invention. Hereby:

[0020]FIG. 1a shows a perspectival top view of a shroud with insertedcover plate,

[0021]FIG. 1b shows a cross-section through the receptacle contour of ashroud with inserted cover plate,

[0022]FIG. 2a,b,c show illustrations of a known cover plate/shroudconnection (state of the art),

[0023]FIG. 3a,b show illustrations of the formation of a tear in thesoldering joint,

[0024]FIG. 4a to c show a shape-mated connection using an inserted part,

[0025]FIG. 5a,b,c show an illustration of alternative joint geometries,

[0026]FIG. 6 shows an illustration of shape-mated connections by meansof mechanical retention means.

WAYS OF EXECUTING THE INVENTION, COMMERCIAL USABILITY

[0027]FIG. 1a shows a perspectival top view of a gas turbine blade witha shroud 2 that is provided at its radially-oriented top side with arectangular recess 10, into which the cover plate 6 is completelyinserted radially from the top. Between the cover plate 6 and the shroud2, a soldering joint 7 is inserted, which completely surrounds thecircumferential contour of the cover plate 6.

[0028]FIG.1b shows a cross-section through an optional pointtransversely to the receptacle contour inside the shroud 2. Thereceptacle contour of the shroud 2 is provided with a first, obliqueradially-oriented stage surface 11, as well as an axially-orientedsecond stage surface, the so-called support surface 12. The depth of thestage of the receptacle contour preferably is selected just so that thesurface of the cover plate 6 ends flush with surface of the shroud 2.Between the cover plate 6 and the shroud 2 a gap 13 is provided forinserting the cover plate 6, the size of said gap being selected atleast so that it enables a simple insertion of the cover plate 6 intothe receptacle contour of the shroud 2 based on an existing installationplay 16. The gap 13 forming between the cover plate 6 and the shroud 2is then filled completely with soldering material 14 and is soldered,whereby the soldering material 14 has the lowest possible ductility orhigh brittleness after the soldering process.

[0029] If a gas turbine blade constructed in this manner is taken intooperation, tears form along the soldering joint 7 because of theexisting brittleness and vibrations. FIG. 3a shows such a tear 15composed of two zig-zag-shaped break surfaces that face each otherdirectly. Since the course of the tear takes on a statisticalprogression and therefore has break surface sections along the breaksurfaces that are angled with respect to the radial direction of the gasturbine blade, and therefore to the centrifugal forces acting on the gasturbine blade, a close meshing between the cover plate 6 and the shroudalong the soldering joint helps to prevent the cover plate 6 from beingable to detach from the shroud 2. In addition, the loose, multi-corneredshape-mated connection permits a seat of the cover plate 6 free ofbending stresses inside the shroud, so that the cover plate 6 is exposedto smaller mechanical tensions and vibrations.

[0030]FIG. 3b shows a joint variation using an additional closing strip16 [sic; should be 17] that is soldered on both sides with two solderingjoints 7, 7′. The closing strip 16 [sic] is made from ahigh-temperature-resistant material that has a much higher ductilitythan the soldering material itself, so that the closing strip 16 [sic]helps to produce a vibration dampening of the cover plate 6 inside theshroud 2.

[0031]FIG. 4a illustrates the insertion process of the cover plate 6 inthe receptacle contour of the shroud 2. An installation play 16 betweenthe shroud 2 and the cover plate 6 ensures an unhindered radialinsertion of the cover plate 6 on the shroud 2. The closing piece 16[sic] has a sufficiently high ductility as well as high-temperatureresistance to be able to transfer the forces occurring between the coverplate 6 and the shroud 2 without damage. FIG. 4c shows the progressionof the forces between the cover plate 6, the closing piece 17, and theshroud 2. Because of the longitudinal gap extension oriented at an angleto the radial direction, the force vectors, indicated by arrows in FIG.4c, act on the closing piece 16 [sic] in such a way that the closingpiece 17 prevents the cover plate 6 from detaching radially from theshroud 2.

[0032]FIG. 5a, b and c show different exemplary embodiments forshape-mated connection between the cover plate 6 and the shroud 2. InFIG. 5a, a radially-oriented gap between the shroud 2 and the coverplate 6 is filled with soldering material. FIG. 5b shows a soldering gapangled radially. In FIG. 5c, the gap between cover plate 6 and shroud 2is constructed radially, and a wedge-shaped soldering point 7 isinserted only in the upper area. The shroud 2 hereby slightly projectsbeyond the cover plate 6 so that a triangular soldering wedge 7 is ableto form between the shroud 2 and the cover plate 6. Studies have shownthat with such a wedge-shaped soldering joint 7, a tear forms in such away as to extend at an angle of approximately 45° C. in relation to theradial direction, and in this way helps to create a stabile shape-matedconnection between the cover plate 6 and the shroud 2.

[0033] All of the previously mentioned exemplary embodiments with asoldering joint in which a tear forms have in common that theshape-mated connection is based on the close meshing of the tear linethat forms in a zig-zag shape.

[0034] Alternatively or in combination with the aforementioned jointconnection, the use of a mechanical retention means between cover plateand shroud may help in creating a shape-mated connection that is stableover the long term and secure. In this context, FIG. 6 shows acorresponding connection cross-section between the cover plate 6 and theshroud 2. Between the shroud 2 and the cover plate 6, a retainer ring 18is inserted, which projects on both sides partially into thecircumferential edge of the cover plate 6, as well as into the shroud 2.Alternatively to using a retainer ring 18, rod-shaped form bodies can beprovided, which can be inserted through lateral mounting openings in theshroud and in the cover plate.

[0035] List of Reference Numerals

[0036]1 Blade hub

[0037]2 Shroud

[0038]3 Groove contour

[0039]4,5 Side edges of shroud

[0040]6 Cover plate

[0041]7 Soldering material

[0042]8,9 Side edges of shroud

[0043]10 Recess

[0044]11 First stage surface

[0045]12 Second stage surface

[0046]13 Gap

[0047]14 Soldering material

[0048]15 Tear

[0049]16 Installation play

[0050]17 Closing element

[0051]18 Mechanical retention means

[0052] K Cooling channels

1. Cooled gas turbine blade with a shroud (2) in which a cooling channelsystem (K) is provided, which is closed off radially to the gas turbineblade with a cover plate (6), characterized in that the cover plate (6)has a circumferential edge, along the entire extension of which thecover plate (6) enters into a continuous shape-mated connection or aplurality of locally limited shape-mated connections with the shroud(2).
 2. Cooled gas turbine blade according to claim 1, characterized inthat the plurality of locally limited shape-mated connections aredistributed evenly along the circumferential edge.
 3. Cooled gas turbineblade according to claim 1 or 2, characterized in that the shroud (6)has a receptacle contour adapted according to the shape and size of thecircumferential edge of the cover plate (2), having a steppedcross-section provided with a radially or oblique radially-orientedfirst (11) and an axially-oriented second stage surface (12), theso-called support surface, and in which the cover plate (6) can be setradially onto the support surface, and that in the area between thefirst stage surface (11) and the circumferential edge of the cover plate(6) a retention means is provided that ensures the shape-matedconnection.
 4. Cooled gas turbine blade according to claim 3,characterized in that a gap (13) is provided between the first stagesurface (11) and the cover plate (6) set into the receptacle contour. 5.Cooled gas turbine blade according to claim 4, characterized in that thefirst stage surface (11) and the circumferential edge are formed in astraight line and that the gap (13) has a largely constant gap width,and that the gap (13) is oriented radially or oblique radially to thelongitudinal direction of the gas turbine blade.
 6. Cooled gas turbineblade according to one of claims 3 to 5, characterized in that theretention means is a joining means that is provided in the area betweenthe first stage surface (11) and the circumferential edge of the coverplate (6) and enters into a close joint connection with both the firststage surface (11) and the circumferential edge, and that within thejoining means, along the extension of both joint connections, at leastone break surface (15) extending completely through the joining means isprovided and has break surface sections extending at an angle to theradial direction.
 7. Cooled gas turbine blade according to claim 6,characterized in that the joining means is a soldering material (7) thathas no ductility or only little ductility.
 8. Cooled gas turbine bladeaccording to one of claims 3 to 6, characterized in that the dimensionsof the first stage surface (11) are such that it projects beyond thecover plate (6) set into the receptacle contour, that the joining meansis provided at least above the cover plate (6) between the cover plate(6) and the first stage surface (11) projecting beyond the cover plate(6), and that the break surface (15) extends through the joining meansradially at an angle.
 9. Cooled gas turbine blade according to claim 8,characterized in that the break surface (15) extends at an angle rangeof approximately 45° C. with respect to the cover plate (6).
 10. Cooledgas turbine blade according to claim 3, characterized in that thecircumferential edge of the cover plate (6) has a mounting contourextending along the circumferential edge, into which mounting contour amechanical retention means (18) can be inserted, and that along thefirst stage surface (11) a mounting contour corresponding to themounting contour of the cover plate (6) is provided, with which themechanical retention means (18) meshes inside the receptacle contour ina force-derived manner in the joined state of the cover plate (6). 11.Cooled gas turbine blade according to claim 10, characterized in thatthe mechanical retention means (18) is a type of retainer ring providedin the mounting contour of the cover plate (6).
 12. Cooled gas turbineblade according to claim 10, characterized in that the mechanicalretention means (18) consists of a plurality of rod-shaped form bodiesthat can be inserted into the mounting contour through lateral mountingopenings in the shroud between the circumferential edge of the coverplate and the first stage surface.